Universe Guide


Z Orionis, HD249313, HIP28045

Z Orionis is a blue eclipsing main sequence dwarf star that can be located in the constellation of Orion. The star can not be seen by the naked eye, you need a telescope to see it.

HIP28045 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD249313.

Z Orionis has alternative name(s), Z Ori.

Location of Z Orionis

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For Z Orionis, the location is 05h 55m 50.93 and +13d41`42.0 .

Proper Motion of Z Orionis

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -4.08 ± 1.06 miliarcseconds/year towards the north and 1.56 ± 1.88 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Z Orionis

Z Orionis has a spectral type of B4V SB. This means the star is a blue main sequence dwarf star. The star has a B-V Colour Index of 0.01 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 9,392 Kelvin. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Z Orionis Apparent and Absolute Magnitudes

Z Orionis has an apparent magnitude of 9.95 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of If you used the 2007 Parallax value, you would get an absolute magnitude of -1.83. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to Z Orionis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as -1.13 which gave the calculated distance to Z Orionis as -2886.40 light years away from Earth or -884.96 parsecs. It would take a spaceship travelling at the speed of light, -2886.40 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 0.44 which put Z Orionis at a distance of 7412.80 light years or 2272.73 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

Variable Type of Z Orionis

The star is a eclipsing Beta Persei (Algol)/Detached Main Sequence with a subgiant (subtype) variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Z Orionis brightness ranges from a magnitude of 10.890 to a magnitude of 9.900 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.2 days (variability).

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Z Orionis Facts

Alternative Names

Traditional/Proper NameZ Orionis
Short NameZ Ori
Hipparcos Library I.D.28045
Bonner DurchmusterungBD+13 1034
Henry Draper Designation249313

Visual Facts

Star Typemain sequence dwarf star
Visual / Apparent Magnitude9.95
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)05h 55m 50.93
Declination (Dec.)+13d41`42.0
Galactic Latitude-5.72 degrees
Galactic Longitude194.35 degrees
1997 Distance from Earth-1.13 Parallax (milliarcseconds)
 -2886.40 Light Years
 -884.96 Parsecs
2007 Revised Distance from Earth0.44 Parallax (milliarcseconds)
 7412.80 Light Years
 2272.73 Parsecs
Proper Motion Dec.-4.08 ± 1.06 milliarcseconds/year
Proper Motion RA.1.56 ± 1.88 milliarcseconds/year
B-V Index0.01
Radial Velocity2.00 ± 10.00 km/s
Spectral TypeB4V SB
Colour(B) blue

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/Detached Main Sequence with a subgiant (subtype)
Mean Variability Period in Days5.203
Variable Magnitude Range (Brighter - Dimmer)9.900 - 10.890

Estimated Facts

Calculated Effective Temperature9,392 Kelvin

Sources and Links

SIMBAD SourceLink

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